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PROGRESS ON LOW ACTIVATION STRUCTURAL STEELS

PROGRESS ON LOW ACTIVATION STRUCTURAL STEELS. RECENT RESULTS ON NANOSTRUCTURED FERRITIC ALLOYS A.F.ROWCLIFFE (ORNL) ARIES PROJECT MEETING U.C.S.D. Jan 22 nd . – Jan 23 rd 2013. Nanostructured Ferritic Alloys (NFAs ). BF-TEM of 14YWT SM10 Heat. < Grain size > = 136 (+/- 14) nm.

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PROGRESS ON LOW ACTIVATION STRUCTURAL STEELS

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  1. PROGRESS ON LOW ACTIVATION STRUCTURAL STEELS RECENT RESULTS ON NANOSTRUCTURED FERRITIC ALLOYS A.F.ROWCLIFFE (ORNL) ARIES PROJECT MEETING U.C.S.D. Jan 22nd. – Jan 23rd 2013

  2. Nanostructured Ferritic Alloys (NFAs) BF-TEM of 14YWT SM10 Heat <Grain size> = 136 (+/- 14) nm Nv = 1-7 x 1023 m-3 <r> = 1.8 (+/- 0.4) nm • Nanograin structure & high density of nanoclusters. • High energy mechanical alloying plus high power consolidation • Very large interfacial area (NC-matrix and grain boundaries) enhances recombination of point defects as well as accommodation of helium atoms or bubbles in irradiation. • In ferritic phase, the nanograins & NCs are exceptionally stable up to very high temperatures. HR-TEM 2

  3. NFAs have outstanding strength and creep properties 12YWT: First discovery of NC by 3DAP in 1999 (ORNL) MA957: Patented by INCO (1978); NC discovered by 3-DAP in 2003 (ORNL) 14YWT: Developed at ORNL; initial project started in 2001 • MA957 and 12YWT are not commercially available • 12YWT was produced only once as a small heat by Kobe Steel, Ltd. • Production of MA957 was discontinued by INCO • M.A.Sokolov, D.T.Hoelzer, L.Tan (ORNL)

  4. FRACTURE TOUGHNESS-STRENGTH PROPERTIES UNIQUE NANO-SCALE MICROSTRUCTURE OF THE LOW ACTIVATION NFA 14YWT CHALLENGES THE HIGH STRENGTH-LOW TOUGHNESS PARADIGM FOR STRUCTURAL ALLOYS D.T.Hoelzer ORNL, unpublished work

  5. Neutron irradiation of 14YWT and 14WT at 300oC, 580oC, and 670oC to ~1.5 dpa (HFIR Rabbit capsules) D.A. McClintock et al., JNM 386-388 (2009)

  6. No DBTT shift was observed in 14YWT after irradiation at 300oC to ~ 1.5 dpa compared to 85oC shift in Eurofer-ODS Eurofer-ODS D.A. McClintock, et al., JNM 392 (2009)

  7. HELIUM MANAGEMENT IN ADVANCED STRUCTURAL ALLOYS TEM images of Eurofer 97 (TMS), (a, b), and MA957 (NFA) (c,d) Neutron irradiated to 25dpa at 500C and simultaneously implanted with ~1450 appm He G.R.Odette et al., Fusion Materials Semi-Annual Report, DOE/ER-0313/51

  8. HELIUM MANAGEMENT IN ADVANCED STRUCTURAL ALLOYS • High helium content (1450appm) promotes the formation of a large population of voids in neutron irradiated Eurofer 97 • Same quantity of helium is trapped by ~2nm clusters/particles in MA957 with no void formation • Swelling rate theory extrapolations indicate that NFA will remain damage-tolerant to much higher levels of dpa and helium • Extrapolations for the TMS indicate continuing growth of voids with eventual transition to a linear (with dose) swelling regime

  9. NFAs WITH IMPROVED FRACTURE RESISTANCE • NFAs based on 12-14% Cr tend to exhibit reduced grain boundary fracture resistance with increasing temperature > 400C • New approaches to NFA fabrication involve controlled phase transformation during high temperature rolling to strengthen grain boundaries while retaining the nano-scale microstructure for high strength and radiation damage resistance • New compositions are based on Fe-9Cr-2W-0.4Ti-0.2V- 0.3 Y2O3 • Initial results from a joint ORNL-KAERI project funded by Office of Nuclear Science and Technology show promise.

  10. MICROSTRUCTURE OF NEW NFAs PM2 PM1 9YWTV-PM2 Fe-9Cr-2W-0.4Ti-0.2V-0.05C+0.3Y2O3 9YWTV-PM1 Fe-9Cr-2W-0.4Ti-0.2V-0.12C-0.3Y2O3 T.S.Byun,D.T.Hoelzer (ORNL), J.H.Koon (KAERI); unpublished work

  11. Strength & Ductility of 9Cr NFAs • New base NFAs retain YS higher than 500 MPa at 700°C. • Improved ductility for both new NFAscompared to 14YWT T.S.Byun, D.T.Hoelzer (ORNL), J.H.Koon (KAERI); unpublished work

  12. Effect of Controlled Rolling 9YWTV-PM on High TemperatureFracture Resistance • Improvement of fracture toughness in controlled rolled 9YWTV-PM2 is significant. • The 9YWTV-PM2 controlled rolled at 900°C for 50% reduction resulted in the best fracture toughness among NFAs, which is as high as those of non-ODS F/M steels. • Potential avenue for NFAs based on 9Cr with improved high temperature fracture resistance T.S.Byun, D.T.Hoelzer ( ORNL ), J.H.Koon (KAERI); unpublished work

  13. Creep performance of NFAs • Creep test on ruptured MA957 started in Oct., 2003 (INE • Creep test on 14YWT-SM10 started in April, 2008 Ruptured after ~38,555 h • Klueh et al, J. Nucl. Mat., (2005) • I-NERI FY01-04

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